How to automate this process (SVG to mesh > planar decimation > solidify > collapse decimation) to 300 files?
This is pretty quick and dirty so be sure to test a small sample 1st, but i think it covers everything you asked for. Running the script will add a toolbar in the 3d view port, the values you had set in the example are properties you can change before importing and exporting all the files in the directories. Have fun with it.

import bpy
import os
from bpy.types import Operator
from bpy.types import Panel
from math import radians

bl_info = {
    "name": "AutoSVG",
    "author": "Your Name Here",
    "version": (1, 0),
    "blender": (2, 79, 0),
    "location": "View3D &gt; Tools panel 'T' &gt; AutoSVG &gt; AutoSVG",
    "description": "",
    "warning": "",
    "wiki_url": "",
    "category": "",
    }


def makeprop():
    bpy.types.Scene.auto_svg_dir_in = bpy.props.StringProperty(
        name="bpy.types.Scene.auto_svg_dir_in",
        description="",
        default="",
        subtype="DIR_PATH",
        )
    bpy.types.Scene.auto_svg_decimate_angle = bpy.props.FloatProperty(
        name="bpy.types.Scene.auto_svg_decimate_angle",
        description="",
        default=radians(0.00174533),
        subtype="ANGLE",
        )
    bpy.types.Scene.auto_svg_thickness = bpy.props.FloatProperty(
        name="bpy.types.Scene.auto_svg_thickness",
        description="",
        default=0.009,
        subtype="DISTANCE",
        unit='LENGTH'
        )
    bpy.types.Scene.auto_svg_ratio = bpy.props.FloatProperty(
        name="bpy.types.Scene.auto_svg_ratio",
        description="",
        default=0.1,
        )
    bpy.types.Scene.auto_svg_rotation = bpy.props.FloatProperty(
        name="bpy.types.Scene.auto_svg_rotation",
        description="",
        default=radians(-1.69297),
        subtype="ANGLE",
        )
    bpy.types.Scene.auto_svg_uv_angle = bpy.props.FloatProperty(
        name="bpy.types.Scene.auto_svg_uv_angle",
        description="",
        default=radians(89),
        subtype="ANGLE",
        )
    bpy.types.Scene.auto_obj_dir_out = bpy.props.StringProperty(
        name="bpy.types.Scene.auto_obj_dir_out",
        description="",
        default="",
        subtype="DIR_PATH",
        )


def delprop():
    del bpy.types.Scene.auto_svg_dir_in
    del bpy.types.Scene.auto_svg_decimate_angle
    del bpy.types.Scene.auto_svg_thickness
    del bpy.types.Scene.auto_svg_ratio
    del bpy.types.Scene.auto_svg_rotation
    del bpy.types.Scene.auto_svg_uv_angle
    del bpy.types.Scene.auto_obj_dir_out


def begin(scene):
    for files in os.listdir(scene.auto_svg_dir_in):
        if not files.endswith(".svg"):
            print("unexpected file type : ", files)
            continue
        bpy.ops.import_curve.svg(
            filepath=str(os.path.join(scene.auto_svg_dir_in, files)))
        bpy.ops.object.select_all(action='DESELECT')
        my_svg = bpy.data.objects['Curve']
        my_svg.select = True
        scene.objects.active = my_svg
        my_svg.name = files.rstrip(".svg")
        bpy.ops.object.convert(target='MESH')
        bpy.ops.object.modifier_add(type='DECIMATE')
        bpy.context.object.modifiers["Decimate"].decimate_type = 'DISSOLVE'
        bpy.context.object.modifiers["Decimate"].angle_limit = (
            scene.auto_svg_decimate_angle)
        bpy.ops.object.modifier_add(type='SOLIDIFY')
        bpy.context.object.modifiers["Solidify"].thickness = (
            scene.auto_svg_thickness)
        bpy.ops.object.modifier_add(type='DECIMATE')
        bpy.context.object.modifiers["Decimate.001"].ratio = (
            scene.auto_svg_ratio)
        bpy.context.object.rotation_euler[1] = scene.auto_svg_rotation
        bpy.ops.object.editmode_toggle()
        bpy.ops.mesh.select_all(action='TOGGLE')
        bpy.ops.uv.smart_project(angle_limit=scene.auto_svg_uv_angle)
        bpy.ops.object.editmode_toggle()
        bpy.ops.export_scene.obj(
            filepath=str(os.path.join(
                scene.auto_obj_dir_out, files.replace(".svg", ".obj"))))
        bpy.ops.object.delete()


class Auto_SVG_Tool():
    @classmethod
    def main(cls, context):
        scene = bpy.context.scene
        print("start button pressed")
        filevalid = ((scene.auto_svg_dir_in is not "") and
                     (scene.auto_obj_dir_out is not ""))
        if not filevalid:
            print("invalid file location or name")
            return
        begin(scene)


class Auto_SVG_Button(bpy.types.Operator):
    """Execute generation"""
    bl_idname = "file.autosvg_operator"
    bl_label = "Generate"

    def execute(self, context):
        Auto_SVG_Tool.main(context)
        return {'FINISHED'}


class VIEW3D_PT_Blank1_Blank2(Panel):
    bl_space_type = 'VIEW_3D'
    bl_region_type = 'TOOLS'
    bl_category = "AutoSVG"
    bl_context = "objectmode"
    bl_label = "AutoSVG"

    def draw(self, context):
        scene = context.scene
        layout = self.layout
        row = layout.row()
        col = layout.column(align=True)
        col.prop(scene, "auto_svg_dir_in", "Input Dir")
        col.separator()
        col.prop(scene, "auto_svg_decimate_angle", "Decimate angle")
        col.prop(scene, "auto_svg_thickness", "Solidify Thickness")
        col.prop(scene, "auto_svg_ratio", "Decimate Ratio")
        col.prop(scene, "auto_svg_rotation", "Object rotation")
        col.prop(scene, "auto_svg_uv_angle", "UV project angle lim")
        col.separator()
        col.prop(scene, "auto_obj_dir_out", "Output Dir")
        col.separator()
        col.operator("file.autosvg_operator", text="Start Files")


def register():
    print("registered")
    bpy.utils.register_class(VIEW3D_PT_Blank1_Blank2)
    bpy.utils.register_class(Auto_SVG_Button)
    makeprop()


def unregister():
    print("un-registered")
    bpy.utils.unregister_class(VIEW3D_PT_Blank1_Blank2)
    bpy.utils.unregister_class(Auto_SVG_Button)
    delprop()

if __name__ == "__main__":
    register()



changes include:
PEP8 compliance check via http://pep8online.com.
Removed several unused options in properties per batFINGER recommendations.
Invert logic in if statements per Dr. Sybren recommendation reducing indents.
Exported to .obj instead of .stl to preserve UV's.
Due to handling of bpy.ops.export_scene.obj() removed debug print commands.
Renamed curves based on imported file name.